be about equal to that of concrete because the pipe diameter for grout 
would be smaller but the velocity of flow could be greater. The opera- 
tional time for actually placing either concrete or grout would be about 
the same; hence, these costs would be similar. 
Another item in the comparison between concrete and grout that 
strongly favors concrete is whether or not a task can be performed 
without formwork. For an encasement operation, grout would require 
formwork of some kind to contain the material. Without formwork the 
grout, being a slurry, would run horizontally while producing little 
vertical rise. Using concrete there is the ability to place the material 
in thicker lifts. Concrete is able to attain a steeper slope than grout 
even when both materials appear equally "stiff" in a mixer. The large 
aggregate in concrete provides an interlocking capability that permits 
self-standing. 
By avoiding the need for formwork, a major at-sea operation is 
eliminated. The additional time and cost for placing formwork could 
conceivably equal that of the operation to place the grout, thus doubling 
the overall cost. Hence, for this feature alone the development effort 
for concrete is justified. 
To summarize, the cost of an encasement operation using concrete 
to cover a large object is given below as a rough estimate: 
Cost 
Materials 
(10,000 cu yd at $30/cu yd) S$ 300,000 
Material supply 
(8 round trips at 2 days each 80,000 
at $5,000/day) 
Equipment rental 
(cement tanks, concrete 
mixers and pumps, batching Woes 
equipment, etc.) 
Caen $30 ,000/day) 2005000 
Set up charges 100,000 
Engineering and Management 300,000 
Profit 250,000 
$2,000,000 
The total cost would be about $2 million. This is a unit price of 
$200/cu yd of concrete in place, which is comparable to typical construc- 
tion costs of about $300/cu yd for concrete structures but far below 
offshore platform costs of about $700/cu yd. 
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